Nitrogen and phosphorus utilization in the cyanobacterium Microcystis aeruginosa isolated from Laguna de Bay, Philippines

Abstract

Phytoplankton supports fisheries and aquaculture production. Its vital role as food for aquatic animals, like mollusks, shrimp, and fish cannot be overemphasized. Because of its contribution as a food source for fish, the growth kinetics of Microcystis aeruginosa, a dominant cyanobacterium in the lake, was studied. The regular occurrence of M. aeruginosa is experienced during the months of May to July or from September to November in Laguna de Bay, the largest freshwater lake in the Philippines. M. aeruginosa was collected from Laguna de Bay, isolated, and established in axenic conditions. Data on the growth kinetic parameters for nitrate-nitrogen and phosphate-phosphorus utilization by M. aeruginosa gave the following values: half-saturation constant (K_s), 0.530 mg N. L⁻¹ and 0.024 mg P. L⁻¹ respectively; maximum growth rate (μ_max), 0.671. d⁻¹ and 0.668. d⁻¹ respectively; maximum cell yield, 6.5 and 6.54 log, cells. ml⁻¹ respectively; nutrient level for saturated growth yield, 8.71 mg N. L⁻¹ and 0.22 mg P. L⁻¹ respectively; and minimum cell quota (Q₀), 2.82 pg N. cell⁻¹ and 0.064 pg P. cell⁻¹ respectively. The low K_s value and high maximum growth rate (μ_max) for phosphorus by M. aeruginosa would suggest a high efficiency of phosphorus utilization. On the other hand, the high K_s value for nitrogen indicated a low rate of uptake for this nutrient.